180-GHz Pulsed CMOS Transmitter for Molecular Sensing

The performance of a CMOS transmitter designed for planetary science in situ molecular sensing applications having an operational bandwidth of 180-190 GHz and peak output power of 0.6 mW (-2.22 dBm) is evaluated with a series of spectroscopic-based experimental trials. Continuous wave frequency modulated absorption schemes are exploited to probe the Doppler and sub-Doppler lineshape profiles of the water rotational transition at 183.310 GHz. These results demonstrate the tuning finesse and phase-noise characteristics of the integrated circuit embedded phase lock loop used to generate coherent mm-wave radiation are sufficient for high-precision molecular spectroscopy applications. A description of the pulse modulator designed into the CMOS circuitry allowing for implementation of sensitive emission-based Fourier transform detection schemes is provided with performance characterized for spectroscopically relevant pulse durations (40-500 ns). Results are accompanied by a spectral analysis of the transmitter pulse signal leakage, where the total isolation is measured to be 22 dB. The first emission-based molecular detections obtained with this source are presented demonstrating viability for this transmitter to be incorporated into future planned resonant cavity enhanced in situ molecular sensing systems.